1. Field of Invention
The invention relates to a piezoelectric ink jet print head, more particularly, to an ink jet print head using a laminated piezoelectric actuator and a method of fabricating the same.
2. Description of Related Art
Conventionally, an ink jet print head using a laminated piezoelectric actuator has been known.
As shown in FIG. 32, an ink jet print head 300 includes a cavity plate 310 formed by stacking substantially rectangular metal plates, in which a plurality of pressure chambers 316, which extend in a direction perpendicular to a longitudinal direction of the cavity plate 310, are formed so as to be aligned in parallel with the longitudinal direction of the cavity plate 310. A plate-like piezoelectric actuator 320 having a substantially rectangular plate shape is bonded to the cavity plate 110 so as to close the pressure chambers 316. A flat flexible cable 330 for connecting with external equipment is bonded on the piezoelectric actuator 320.
As shown in FIGS. 32 and 33, a plurality of surface electrodes 326, 327 are provided on the piezoelectric actuator 320 at its surface opposite to the surface to be bonded to the cavity plate 310 (an upper surface of the plate-type piezoelectric actuator 320 in FIG. 32). The surface electrodes 326 and 327 are formed on both sides and are connected with driving electrodes and common electrodes, respectively. An oval ink supply hole 319 is provided at a left end portion of the cavity plate 310.
According to the conventional piezoelectric actuator, if the piezoelectric sheet is too thin, metallic material in internal electrodes may be diffused too much during sintering of the piezoelectric sheet. This results in piezoelectric characteristic of the piezoelectric sheet being spoiled.
On the other hand, if the piezoelectric sheet is too thick, restraint of non-active portions have a great effect on active portions. Accordingly, the active portions cannot sufficiently deform.
Further, if the internal electrode is too thin, the electrode becomes too narrow or is cut off due to the diffusion of the metallic material during sintering of the piezoelectric sheet. On the other hand, if the internal electrode is too thick, delamination frequently occurs in an interface between portions having the internal electrodes and portions not having the internal electrodes, because there is a great difference in the thickness of the piezoelectric sheets after lamination.
Referring to FIGS. 34 and 35, adhesion of the plate-like piezoelectric actuator 320 onto the cavity plate 310 in the ink jet print head 300 structured as described above will be described. First, as shown in FIG. 34, the cavity plate 310 is placed on a workbench 370 having a flat surface. Next, the piezoelectric actuator 320, to which an adhesive is applied at its bottom, is placed on the cavity plate 310 on the workbench 370, while checking to make sure that the cavity plate 310 is in proper alignment with the piezoelectric actuator 320. Then, as shown in FIG. 35, a force of 10 kg-weight is applied to the upper surface of the piezoelectric actuator 320, in a direction indicated with an arrow A, using an assembly jig 340 having a flat bottom surface. Thus, the piezoelectric actuator 320 is bonded to the cavity plate 310.
However, in the above-described method of adhering the plate-like piezoelectric actuator 320 to the cavity plate 310, the assembly jig 340 only presses the surface electrodes 326, 327 provided on the surface of the piezoelectric actuator 320. As shown in FIGS. 34 and 35, when there are waves 320a, which are smaller than the thickness of the surface electrodes 326, 327, in a middle of the piezoelectric actuator 320, the waves 320a cannot be flatted using the assembly jig 340. If the waves 320a remain in the piezoelectric actuator 320, an adhesion failure may occur in the piezoelectric actuator 320 and the cavity plate 310. Ink leakage may also occur.
The piezoelectric ink jet print head as described above is typically produced by the following method. First, internal electrodes are screen-printed on piezoelectric sheets, and the piezoelectric sheets having the electrodes and the piezoelectric sheets not having the electrodes are alternatively stacked. The laminated piezoelectric sheets are pressed and sintered. After that, a deformation restraining member is bonded to the laminated piezoelectric sheets using an adhesive.
Further, the piezoelectric actuator fabricated as described above is bonded to the cavity plate having pressure chambers. Finally, the piezoelectric ink jet print head is obtained.
When the piezoelectric actuator is fabricated using such a conventional method, asperities are developed in the surfaces of the piezoelectric actuator and the cavity plate, which are adhered each other, after sintering of the piezoelectric sheets. As a result, an adhesion failure may occur in the piezoelectric actuator and the cavity plate.
Accordingly, grinding is required to be performed on the surface of the piezoelectric actuator after sintering. All of the above lead to problems in operating efficiency and costs in the production and use of piezoelectric ink jet printheads.
In light of the foregoing, it would be desirable to provide a piezoelectric ink jet print head using a laminated piezoelectric actuator that addresses the foregoing drawbacks associated with other known piezoelectric ink jet print heads.
One aspect of the invention involves a piezoelectric print head that includes a cavity plate and a plate-like piezoelectric actuator. The cavity plate includes a plurality of nozzles and a plurality of pressure chambers communicating with the respective nozzles. The plate-like piezoelectric actuator is formed into a single laminated structure by laminating a plurality of piezoelectric sheets including a plurality of electrodes which are formed at positions so as to be aligned with the respective pressure chambers. The laminated piezoelectric actuator is then sintered and bonded to the cavity plate so as to close the pressure chambers provided in the cavity plate. In the piezoelectric ink jet print head, each of the piezoelectric sheets has a thickness of between 5-40 xcexcm, preferably between 15-30 xcexcm.
According to another aspect of the invention, a piezoelectric ink jet print head includes a cavity plate, a plate-like piezoelectric actuator, surface electrodes and protrusions. The cavity plate includes a plurality of nozzles and a plurality of pressure chambers communicating with the respective nozzles. The plate-like piezoelectric actuator is formed into a single laminated structure by laminating a plurality of piezoelectric sheets including a plurality of electrodes which are formed at positions so as to be aligned with the respective pressure chambers. The laminated piezoelectric actuator is then sintered and bonded to the cavity plate so as to close the pressure chambers provided in the cavity plate. The surface electrodes are provided at an end portion of a surface of the piezoelectric actuator, which is opposed to a surface of the piezoelectric actuator to be bonded to the cavity plate, and are electrically connected with the plurality of electrodes. Each of the protrusions has a thickness of the surface electrodes and is provided on the surface of the piezoelectric actuator where the surface electrodes are provided.
According to yet another aspect of the invention, a piezoelectric ink jet print head includes a cavity plate and a plate-like piezoelectric actuator. The cavity plate includes a plurality of nozzles and a plurality of pressure chambers communicating with the respective nozzles. The plate-like piezoelectric actuator is formed into a single laminated structure by laminating a plurality of piezoelectric sheets including a plurality of electrodes which are formed at positions so as to be aligned with the respective pressure chambers. The laminated piezoelectric actuator is then sintered and bonded to the cavity plate so as to close the pressure chambers provided in the cavity plate. The piezoelectric actuator has a flatness of 30 xcexcm or less, which is a difference of height between projections and depressions formed on the piezoelectric actuator at its surface to which the cavity plate is bonded.